Contact planarization using nanoporous silica materials

ABSTRACT

A process for forming a substantially planarized nanoporous dielectric silica coating on a substrate suitable for preparing a semiconductor device, and semiconductor devices produced by the methods of the invention. The process includes the steps of applying a composition that includes at least one silicon-based dielectric precursor to a substrate, and then, 
     (a) gelling or aging the applied coating, 
     (b) contacting the coating with a planarization object with sufficient pressure to transfer a planar impression to the coating without substantially impairing formation of desired nanometer-scale pore structure, 
     (c) separating the planarized coating from the planarization object, 
     (d) curing said planarized coating; 
     wherein steps (a)-(d) are conducted in any one of the following sequences: 
     (a), (b), (c) and (d); 
     (a), (d), (b) and (c); 
     (b), (a), (d) and (c); and 
     (b), (c), (a) and (d).

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.09/392,413, filed Sep. 9, 1999, now U.S. Pat. No. 6,589,889.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices, includingintegrated circuit (“IC”) devices. More particularly, it relates to amethod for planarizing and/or patterning surfaces of semiconductordevices that contain silica dielectric coatings and particularlynanoporous silica dielectric coatings, as well as to semiconductordevices produced by these methods.

BACKGROUND OF THE INVENTION

Processes used for the fabrication of semiconductor devices almostinvariably produce surfaces which significantly deviate from a planarconfiguration. With the trend toward greater large scale integration,this problem is expected to increase. For instance, the production ofintegrated circuits typically requires multiple layers to be formedsequentially on a semiconductor substrate. Many of these layers arepatterned by selective deposition or selective removal of particularregions of each such layer. It is well known that small deviations fromthe planar condition in underlying layers become more pronounced withthe addition of multiple additional layers of semiconductor and circuitfeatures. Non-planar substrate surfaces can cause many problems thatadversely impact the yield of finished products. For example, variationsin interlevel dielectric thickness can result in failure to open vias,poor adhesion to underlying materials, step coverage, undesirable bendsor turns in conductive metal layers, as well as “depth-of-focus”problems for optical lithography.

In order to effectively fabricate multiple layers of interconnects ithas become necessary to globally planarize the surface of certain layersduring the multi-step process. Planarizing smoothes or levels thetopography of microelectronic device layers in order to properly patternthe increasingly complex integrated circuits. IC features produced usingoptical or other lithographic techniques require regional and globaldielectric planarization where the lithographic depth of focus isextremely limited, i.e., at 0.35 μm and below. As used herein, the term“local planarization” refers to a condition wherein the film is planaror flat over a distance of 0 to about 5 linear micrometers. “Regionalplanarization” refers to a condition wherein the film is planar or flatover a distance of about 5 to about 50 linear micrometers. “Globalplanarization” refers to a condition wherein the film is planar or flatover a distance of about 50 to about 1000 linear micrometers. Withoutsufficient regional and global planarization, the lack of depth of focuswill manifest itself as a limited lithographic processing window.

In addition, as IC feature sizes approach 0.25 μm and below, problemswith interconnect RC delay, power consumption and signal cross-talk havebecome increasingly difficult to resolve. The integration of lowdielectric constant materials for interlevel dielectric (ILD) andintermetal dielectric (IMD) applications, is helping to solve theseproblems. One type of such low dielectric constant materials arenanoporous films prepared from silica, i.e., silicon-based materials.When air, with a dielectric constant of 1, is introduced into a suitablesilica material having a nanometer-scale pore structure, dielectricfilms with relatively low dielectric constants (“k”), e.g., 3.8 or less,can be prepared on substrates, such as silicon wafers, suitable forfabricating integrated circuits. Thus, it is now important for thefabrication of the latest types of semiconductor devices, includingintegrated circuits, to provide methods for planarizing surfaces coatedwith nanoporous silica dielectric films.

One previously employed method of planarization is the etch-backtechnique. In that process, a material, i.e., a planarizing material, isdeposited on a surface in a manner adapted to form a surface relativelyfree of topography. If the device layer and the overlying material layerhave approximately the same etch rate, etching proceeds through theplanarizing material and into the device layer with the surfaceconfiguration of the planarizing layer being transferred to the devicematerial surface. Although this technique has been adequate for someapplications where a modest degree of planarity is required, presentplanarizing materials and present methods for depositing the planarizingmaterial are often inadequate to furnish the necessary planar surfacefor demanding applications such as in submicron device fabrication.

The degree of planarization is defined as the difference between thedepth of the topography on the device surface h_(t), and the verticaldistance between a high point and a low point on the overlying materialsurface h_(d), divided by the depth of the topography on the devicesurface h_(t): $\frac{h_{t} - h_{d}}{h_{t}}$

The degree of planarization, in percent, is$\frac{h_{t} - h_{d}}{h_{t}} \times 100$

Generally, for typical device configurations, planarization using theetch-back technique has not been better than approximately 55% ascalculated by the method described above for features greater than 300microns in width. The low degree planarization achieved by thistechnique is attributed to a lack of planarity in the planarizingmaterial. Thus, for elongated gap-type features greater than 300 micronsin width and 0.5 microns in depth, the usefulness of an etch-backtechnique has been limited.

U.S. Pat. No. 5,736,424, incorporated herein by reference in itsentirety, describes a method for planarizing surfaces of substrates,such as semiconductor materials, by adding a pressing step to anetch-back process. In this reference, an optically flat surface isimpressed on a curable viscous polymer coating on the substrate surfacein need of planarization, followed by polymerization of the coating. Thepolymer is selected to etch at the same rate as the surface in need ofplanarization, and the polymer coating is etched down to the substrate,which is planarized by the process. While an improved planarization isclaimed, apparently by starting the etch-back with a flatter surface, anadded process step and complexity is required. In addition, thisreference fails to provide a solution for planarizing substrates coatedwith nanoporous dielectric films, since by their nature, such lowdensity films cannot be etched at the same rate as the underlyingsubstrate.

Chemical mechanical polishing (CMP) is another known method that hasbeen effectively used in the art to globally planarize the entiresurface of dielectric layers. According to this method, a grainychemical composition or slurry is applied to a polishing pad and is usedto polish a surface until a desired degree of planarity is achieved. CMPcan rapidly remove elevated topographical features without significantlythinning flat areas. However, CMP does require a high degree of processcontrol to obtain the desired results.

Dielectric films formed of organic polymers, such as polyarylene etherand/or fluorinated polyarylene ether polymers, have been planarized byapplying CMP to a partially cured film, followed by a final curing, asdescribed in co-owned U.S. application Ser. No. 09/023,415, filed onFeb. 13, 1998, the disclosure of which is incorporated by referenceherein in its entirety. However, this reference fails to disclose how toplanarize a silicon-based nanoporous dielectric material on the surfaceof a substrate.

For all of these reasons, there remains a need in the art for improvedmethods for achieving the planarization of substrates bearing nanoporoussilica dielectric type materials.

SUMMARY OF THE INVENTION

In order to solve the above mentioned problems and to provide otherimprovements, the invention provides novel methods for effectivelyproducing planarized nanoporous silica dielectric films with a lowdielectric constant (“k”), e., typically ranging from about 1.5 to about3.8, and compositions produced by these methods, having surfaces that donot deviate from a planar topography by more than 0.35μ, and having adegree of planarization of at least 55%, or greater.

Nanoporous silica films can be fabricated by using a mixture of asolvent composition and a silicon-based dielectric precursor, e.g., aliquid material suitable for use as a spin-on-glass (“SOG”) material,which is deposited onto a wafer by conventional methods of spin-coating,dip-coating, etc., and/or by chemical vapor deposition and relatedmethods, as mentioned in detail above. The silica precursor ispolymerized by chemical and/or thermal methods until it forms a gel.Further processing by solvent exchange, heating, electron beam, ionbeam, ultraviolet radiation, ionizing radiation and/or other similarmethods that result in curing and hardening of the applied film.

At an appropriate point in the process, the applied film is contactedwith a planarization object, e., an object with a flat surface, or othertype of surface suitable for the purpose. The planarization object andfilm are brought together with a force sufficient to effectively flattenthe surface of the film, and thereafter the planarization object isseparated from contact with the dielectric film, and any remainingprocess steps are conducted to produce a hardened nanoporous dielectricsilica film.

Thus, the processes and compositions of the invention provide asubstantially planarized nanoporous dielectric silica coating on asubstrate formed by a process that includes: applying a composition thatcomprises a silicon-based precursor onto a substrate to form a coatingon said substrate, and conducting the following steps:

(a) gelling or aging the applied coating,

(b) contacting the coating with a planarization object with sufficientpressure to transfer an impression of the object to the coating withoutsubstantially impairing formation of desired nanometer-scale porestructure,

(c) separating the planarized coating from the planarization object,

(d) curing said planarized coating;

wherein steps (a)-(d) are conducted in a sequence selected from thegroup consisting of

(a), (b), (c) and (d);

(a), (d), (b) and (c);

(b), (a), (d) and (c);

(b), (a), (c) and (d); and

(b), (c), (a) and (d);

The processes and compositions of the invention also provide ananoporous dielectric silica coating on a substrate with a patternimpressed thereon by a process that includes: coating a substrate with acomposition including a precursor for forming a nanoporous dielectricfilm, contacting the coating with a desired patterned surface with apressure and for a time period sufficient in impress the pattern on saidcoating, and then separating the patterned surface from the coating.Optionally, the coating is aged or gelled before, during or after beingcontacted with the patterned surface, and, as noted above, the patternedsurface can also be planar, or include multiple planar regions and/orother desirable features. The treated film can also be cured before,during or after pressing, using heat or any other art-known curingmethods. If the curing is accomplished by heating, the heating can beapplied by any art-standard devices, including a hot plate, a furnace,and even within the press, by applying heat to the film. Simply by wayof example, for curing in a furnace, the heat can be applied at atemperature ranging from about 350° C. to about 600° C. for a timeperiod ranging from about 30 sec to about 5 minutes.

In a further optional feature, the coating to be impressed with one ormore planar surfaces and/or other useful topography and can includedielectric coatings, e.g., silicon-based dielectric coatings, which arenot nanoporous. Thus, dielectric coatings on a substrate that are notfoamed or porous can also optionally be planarized or impressed by themethods described herein.

Processes for producing the above-described nanoporous dielectric silicafilms, as well as integrated circuit devices incorporating theseimproved films, are also provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Accordingly, methods for planarizing substrates and devices areprovided, together with devices fabricated by the inventive methods.

In order to better appreciate the scope of the invention, it should beunderstood that unless the “SiO₂” functional group is specificallymentioned when the term “silica” is employed, the term “silica” as usedherein, for example, with reference to nanoporous dielectric films, isintended to refer to dielectric films prepared by the inventive methodsfrom an organic or inorganic glass base material, e.g., any suitablestarting material containing one or more silicon-based dielectricprecursors. It should also be understood that the use of singular termsherein is not intended to be so limited, but, where appropriate, alsoencompasses the plural, e.g., exemplary processes of the invention maybe described as applying to and producing a “film” but it is intendedthat multiple films can be produced by the described, exemplified andclaimed processes, as desired. Additionally, the term “aging” refers tothe gelling or polymerization, of the combined composition on thesubstrate after deposition, induced, e.g., by exposure to water and/oran acid or base catalyst. The term “curing” refers to the hardening anddrying of the film, after gelling, typically by the application of heat,although any other art-known form of curing may be employed, e.g., bythe application of energy in the form of an electron beam, ultravioletradiation, and the like.

The terms, “agent” or “agents” herein should be considered to besynonymous with the terms, “reagent” or “reagents,” unless otherwiseindicated.

Further, although the description provided herein generally describesprocesses employed for preparing and planarizing foamed dielectricmaterials, such as the exemplified nanoporous silica films, the artisanwill readily appreciate that the instantly provided methods andcompositions are optionally applied to other substrate surfaces, andthat other planarizing materials can be employed, including, forexample, nonporous silica dielectric films.

In addition, the terms, “flat” or “planar” are intended to beequivalent, unless other stated, when used herein. When these terms areemployed with reference to a dielectric film produced by the inventivemethods, it is to indicate that the film has the desired degree ofplanarization.

Of course, it will be appreciated that the exact nature of any surfacefeatures impressed or pressed onto a nanoporous silica-type dielectricfilm will depend on the device requirements and fabrication needs forthe desired resulting integrated circuit device. Thus, any type ofpattern may be impressed upon a nanoporous silica-type dielectric filmaccording to the invention, including multiple planar regions, vias,trenches and the like, for convenience in fabrication. Thus, absent anystatement to the contrary, reference herein to a “planarization object”and/or “planarization surface” is intended to encompass objects orsurfaces bearing any such useful pattern to be impressed on a nanoporousdielectric silica film.

In addition, any suitable number of types of art-known objects can beused as planarization objects to apply a patterned, i.e., including aflat or planar impression, on a plastic or malleable surface, including,for example, objects having at least one flat surface, such as opticalflats and the like, as well as objects possessing a contact surface thatis curved in one of its dimensions, including drums or roller typeobjects, as well as objects having more complex curved surfaces. Thus,for planarization objects having curved surfaces, it will be appreciatedthat contact between such a curved surface and the surface to be treatedwill be achieved with a rolling motion or rotating motion.

As summarized in the “Background of the Invention” above, a number ofmethods for the preparation of nanoporous silica films on substrates areknown to the art. In addition, a number of methods for planarizingsubstrates for the production of integrated circuit (“IC”) devices, arealso known. However, it is believed that prior to the present invention,the successful application of the planarization methods to nanoporousdielectric silica films, as described herein, has not been reported.

Broadly, a substrate coating can be contacted with a planarizationobject before, during or after the aging and/or curing of the appliednanoporous silica dielectric film.

It is simply required that the applied film or coating be sufficientlyplastic or pliable to accept the planar impression, without damaging orpreventing formation of the nanometer-scale pore structure.

It will also be appreciated that the planarization processes provided bythe invention can optionally provide a nanoporous dielectric silica filmhaving a sealed film surface, which can provide the added benefits ofimproved mechanical properties, e g., increased cohesive strength,modulus, or adhesion, relative to nonplanarized films, and optionallycan obviate a need for post-curing surface modification to enhancesurface hydrophobic properties.

Methods for Preparing Planarized Nanoporous Dielectric Films

Typically, nanoporous silica dielectric films are prepared from asuitable silicon-based dielectric precursor, e.g., an S.O.G. materialblended with one or more solvents and/or other components. Thesilicon-based dielectric precursor is applied to a surface to beplanarized by any art-known method, e.g., including, but not limited to,the art-known methods for application of liquid precursors byspin-coating, dip coating, brushing, rolling, spraying and/or bychemical vapor deposition. Prior to application of the base materials toform the nanoporous silica film, the substrate surface is optionallyprepared for coating by standard, art-known cleaning methods.

After the silicon-based dielectric precursor is applied to the substratesurface, the coated surface is contacted with a planarization object.Preferably, the contact surface of the object is fabricated or coatedwith a non-stick release material, e.g., Teflon™ or its functionalequivalent. As noted above, the artisan will also appreciate that thecontact surface, including the described non-stick release material,need not be optically flat, but can also be patterned in order totransfer or imprint any desired topography onto the impressed surface,in the form of multiple planar regions, or other desirable features.

Optionally, the non-stick surface is in the form of a selectivelypermeable membrane, e.g., Gortex™ that is able to pass vapor phasereagents, dissolved gases, reaction product gases, and/or solvents intoor away from the surface being planarized. Advantageously, such anoptional selectively permeable membrane can prevent the formation ofbubble artifacts on or within the planarized surface. Such a selectivelypermeable non-stick surface can also optionally be replaced orundercoated with a material that is selected to absorb and/or adsorbgases or vapors that might lead to undesirable formation of bubbles onthe pressed surface. In another option, the contact surface incorporatesone or more openings or passages to allow for venting of any excessvapors or gases.

Once the surface of the treated dielectric film has assumed the desiredshape, the planarization object and the film are then separated,although in certain embodiments the non-stick release material can beleft on the substrate coating for an additional time period, to allowmore time for aging or gelation, to allow for further film processingand/or to protect the newly planarized surface during further processingsteps.

The processes and compositions of the invention are provided in greaterdetail, as follows.

Silicon-Based Precursors for Dielectric Films

Preferred silicon-based dielectric precursors include organosilanes,including, for example, alkoxysilanes according to Formula I, as taught,e.g., by co-owned U.S. application Ser. No. 09/054,262, filed on Apr. 3,1998, the disclosure of which is incorporated by reference herein in itsentirety.

In one embodiment, Formula I is an alkoxysilane wherein at least 2 ofthe R groups are independently C₁ to C₄ alkoxy groups, and the balance,if any, are independently selected from the group consisting ofhydrogen, alkyl, phenyl, halogen, substituted phenyl. For purposes ofthis invention, the term alkoxy includes any other organic group whichcan be readily cleaved from silicon at temperatures near roomtemperature by hydrolysis. R groups can be ethylene glycoxy or propyleneglycoxy or the like, but preferably all four R groups are methoxy,ethoxy, propoxy or butoxy. The most preferred alkoxysilanesnonexclusively include tetraethoxysilane (TEOS) and tetramethoxysilane.As exemplified below, a partially hydrolyzed and partially condensedfluid alkoxysilane composition can be employed. Such a precursor iscommercially available as Nanoglass™ K2.2 (AlliedSignal, Inc., AdvancedMicoelectronic Materials).

In a further option, for instance, especially when the precursor isapplied to the substrate by chemical vapor deposition, e.g., as taughtby co-owned patent applicatiion Ser. No. 09/111,083, filed on Jul. 7,1998, and incorporated by reference herein in its entirety, theprecursor can also be an alkylalkoxysilane as described by Formula I,but instead, at least 2 of the R groups are independently C₁ to C₄alkylalkoxy groups wherein the alkyl moiety is C₁ to C₄ alkyl and thealkoxy moiety is C₁ to C₆ alkoxy, or ether-alkoxy groups; and thebalance, if any, are independently selected from the group consisting ofhydrogen, alkyl, phenyl, halogen, substituted phenyl. In one preferredembodiment each R is methoxy, ethoxy or propoxy. In another preferredembodiment at least two R groups are alkylalkoxy groups wherein thealkyl moiety is C₁ to C₄ alkyl and the alkoxy moiety is C₁ to C₆ alkoxy.In yet another preferred embodiment for a vapor phase precursor, atleast two R groups are ether-alkoxy groups of the formula (C₁ to C₆alkoxy)_(n) wherein n is 2 to 6.

Application Ser. No. 09/111,083, mentioned above, also teaches thatpreferred silica precursors for chemical vapor deposition include, forexample, any or a combination of alkoxysilanes such astetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane,tetra(methoxyethoxy)silane, tetra(methoxyethoxyethoxy)silane which havefour groups which may be hydrolyzed and than condensed to producesilica, alkylalkoxysilanes such as methyltriethoxysilane silane,arylalkoxysilanes such as phenyltriethoxysilane and precursors such astriethoxysilane which yield SiH functionality to the film.Tetrakis(methoxyethoxyethoxy)silane, tetrakis(ethoxyethoxy)silane,tetrakis(butoxyethoxyethoxy)silane, tetrakis(2-ethylthoxy)silane,tetrakis(methoxyethoxy)silane, and tetrakis(methoxypropoxy)silane areparticularly useful for the invention. Additionally, partiallyhydrolyzed, condensed or polymerized derivatives of these species can beused in this invention. Other precursors of utility to this inventioncould include precursors which can be thermally or photolyticallycrosslinked. In general, the precursors can be gases, liquids or solidsat room temperature.

In other preferred embodiments, the silicon-based dielectricprecursor(s) can also be selected from one or more additional polymers,as taught by co-owned U.S. application serial No. 60/098,515, filed onAug. 31, 1998, and incorporated by reference herein in its entirety,including, but not limited to, a silsesquioxane polymer,hydrogensiloxanes which have the formula [(HSiO_(1.5))_(x)O_(y)]_(n),hydrogensilsesquioxanes which have the formula (HSiO_(1.5))_(n), andhydroorganosiloxanes which have the formulae[(HSiO_(1.5))_(x)O_(y)(RSiO_(1.5))_(z)]_(n),[(HSiO_(1.5))_(x)(RSiO_(1.5))_(y)]_(n) and[(HSiO_(1.5))_(x)O_(y)(RSiO_(1.5))_(z)]_(n). In each of these polymerformulae, x is about 6 to about 20, y is 1 to about 3, z is about 6 toabout 20, n ranges from 1 to about 4,000, and each R is independently H,C₁ to C₈ alkyl or C₆ to C₁₂ aryl. The weight average molecular weightmay range from about 1,000 to about 220,000. In the preferred embodimentn ranges from about 100 to about 800 yielding a molecular weight of fromabout 5,000 to about 45,000. More preferably, n ranges from about 250 toabout 650 yielding a molecular weight of from about 14,000 to about36,000. Thus, useful silicon-based polymers nonexclusively includehydrogensiloxane, hydrogensilsesquioxane, hydrogenmethylsiloxane,hydrogenethylsiloxane, hydrogenpropylsiloxane, hydrogenbutylsiloxane,hydrogentertbutylsiloxane, hydrogenphenylsiloxane,hydrogenmethylsilsesquioxane, hydrogenethylsilsesquioxane,hydrogenpropylsilsesquioxane, hydrogenbutylsilsesquioxane,hydrogentert-butylsilsesquioxane and hydrogenphenylsilsesquioxane andmixtures thereof, as well as others too numerous to mention.

In further preferred embodiments, as taught by co-owned U.S. serial No.60/098,068, filed on Aug. 27, 1998, incorporated by reference herein inits entirety, the silica precursor(s) can also be formed by reactingcertain multifunctional silane reagents prior to application of thereaction product to a substrate. For example, such precursors are formedby reacting a multifunctional, e.g., a trifunctional silane precursor,with a tetrafunctional silane precursor and then depositing the reactionproduct on a substrate.

Desirable multi-functional alkoxysilanes are selected from the grouphaving the formula

A_(n)—SiH_(m)  Formula II

wherein each A is independently an alkoxy (O—R) wherein R is an organicmoiety independently selected from the group consisting of an alkyl andan aryl, and wherein n is an integer ranging from 1 to 3; m is aninteger ranging from 1 to 3 and the sum of m and n is 4.

A tetrafunctional alkoxylsilane employed in the processes of theinvention preferably has a formula of

A₄—Si  Formula III

wherein each A is independently an alkoxy (O—R) and R is an organicmoiety independently selected from the group consisting of an alkyl andan aryl,

In a further aspect of the invention, the alkoxysilane compoundsdescribed above may be replaced, in whole or in part, by compounds withacetoxy and/or halogen-based leaving groups. For example, the precursorcompound may be an acetoxy (CH₃—CO—O—) such as an acetoxy-silanecompound and/or a halogenated compound, e.g., a halogenated silanecompound and/or combinations thereof. For the halogenated precursors thehalogen is, e.g., Cl, Br, I and in certain aspects, will optionallyinclude F.

Generally for the above-described base materials or dielectric filmprecursors, the polymer component is preferably present in an amount offrom about 10% to about 50% by weight of the composition. A morepreferred range is from about 15% to about 30% and most preferably fromabout 17% to about 25% by weight of the composition. Preferred siloxanematerials are commercially available, for example, from AlliedSignalInc. under the tradename Accuglas®.

Substrates

Broadly speaking, a “substrate” as described herein includes anysuitable composition formed before a nanoporous silica film of theinvention is applied to and/or formed on that composition. For example,a substrate is typically a silicon wafer suitable for producing anintegrated circuit or related device, and the base material from whichthe nanoporous silica film is formed is applied onto the substrate byconventional methods, e.g., including, but not limited to, the art-knownmethods of spin-coating, dip coating, brushing, rolling, spraying and/orchemical vapor deposition, or other suitable method or methods. Prior toapplication of the base materials to form the nanoporous silica film,the substrate surface is optionally prepared for coating by standard,art-known cleaning methods.

Suitable substrates for the present invention non-exclusively includesemiconductor materials such as gallium arsenide (“GaAs”), silicon andcompositions containing silicon such as crystalline silicon,polysilicon, amorphous silicon, epitaxial silicon, and silicon dioxide(“SiO₂”) and mixtures thereof. The substrate is typically prepared orobtained, prior to further processing, in the form of a polished wafer.On the surface of the substrate is an optional pattern of raised lines,such as metal, oxide, nitride or oxynitride lines which are formed bywell known lithographic techniques. Suitable materials for the linesinclude silica, silicon nitride, titanium nitride, tantalum nitride,aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten andsilicon oxynitride. These lines form the conductors or insulators of anintegrated circuit.

Such are typically closely separated from one another at distances ofabout 20 micrometers or less, preferably 1 micrometer or less, and morepreferably from about 0.05 to about 1 micrometer. Other optionalfeatures of the surface of a suitable substrate include an oxide layer,such as an oxide layer formed by heating a silicon wafer in air, or morepreferably, an SiO₂ oxide layer formed by chemical vapor deposition ofsuch art-recognized materials as, e.g., plasma enhancedtetraethoxysilane (“PETEOS”) silane oxide and combinations thereof, aswell as one or more previously formed nanoporous silica dielectricfilms.

The nanoporous silica films of the invention can be applied so as tocover and/or lie between such optional electronic surface features,e.g., circuit elements and/or conduction pathways that may have beenpreviously formed features of the substrate. Such optional substratefeatures can also be applied above the nanoporous silica film of theinvention in at least one additional layer, so that the low dielectricfilm serves to insulate one or more, or a plurality of electricallyand/or electronically functional layers of the resulting integratedcircuit. Thus, a substrate according to the invention optionallyincludes a silicon material that is formed over or adjacent to ananoporous silica film of the invention, during the manufacture of amultilayer and/or multicomponent integrated circuit.

In a further option, a substrate bearing a nanoporous silica film orfilms according to the invention can be further covered with additionallayers.

A. Applying Silicon-Based Dielectric Precursor to a Substrate

Nanoporous silica dielectric films are prepared by coating asilicon-based dielectric precursor onto a substrate or substrates usingmethods based upon those described in detail in, for example, inco-owned U.S. application Ser. No. 09/054,262, filed on Apr. 3, 1998,the disclosure of which is incorporated by reference herein in itsentirety. Modifications to methods described in U.S. application Ser.No. 09/054,262, for example, include those that are those optionallyrequired by the need for contacting the film material with aplanarization object.

Typically, a nanoporous silica dielectric film is prepared by forming areaction product of, for example, at least one alkoxysilane, e.g., asdescribed by Formula I, supra, a solvent composition, optional water andan optional catalytic amount of an acid or base. Water is included toprovide a medium for hydrolyzing the alkoxysilane. Preferably thesolvent composition comprises at least one relatively high volatilitysolvent and at least one a relatively low volatility solvent.

This reaction product is applied onto a substrate optionally havingraised lines e.g., as described supra. The high volatility solventevaporates during and immediately after deposition of the reactionproduct. The reaction product is hydrolyzed and condensed until it formsa gel layer. For planarization, for example, a flat surface can becontacted with the gel layer after the high volatility solvent hasevaporated, leaving behind a viscous coating, but before the curing oraging process has progressed sufficiently to render the coatingnon-pliable.

For purposes of the invention, “a relatively high volatility solvent” isone which evaporates at a temperature below, preferably significantlybelow that of the relatively low volatility solvent. The relatively highvolatility solvent preferably has a boiling point of about 120° C. orless, preferably about 100° C. or less. Suitable high volatilitysolvents nonexclusively include methanol, ethanol, n-propanol,isopropanol, n-butanol and mixtures thereof. Other relatively highvolatility solvent compositions which are compatible with the otheringredients can be readily determined by those skilled in the art.

For purposes of the invention, “a relatively low volatility solvent”composition is one which evaporates at a temperature above, preferablysignificantly above, that of the relatively high volatility solvent. Therelatively low volatility solvent composition preferably has a boilingpoint of about 175° C. or higher, more preferably about 200° C. orhigher. Suitable low volatility solvent compositions nonexclusivelyinclude alcohols and polyols including glycols such as ethylene glycol,1,4-butylene glycol, 1,5-pentanediol, 1,2,4-butanetriol,1,2,3-butanetriol, 2-methyl-propanetriol,2-(hydroxymethyl)-1,3-propanediol, 1,4,1,4-butanediol,2-methyl-1,3-propanediol, tetraethylene glycol, triethylene glycolmonomethyl ether, glycerol and mixtures thereof. Other relatively lowvolatility solvent compositions which are compatible with the otheringredients can be readily determined by those skilled in the art.

In another option, acid catalysts can be employed. Suitable acids arenitric acid and compatible organic acids which are volatile, i.e. whichevaporate from the resulting reaction product under the processoperating conditions, and which do not introduce impurities into thereaction product.

The silane component, e.g., alkoxysilane, is preferably present in anamount of from about 3% to about 50% by weight of the overall blend. Amore preferred range is from about 5% to about 45% and most preferablyfrom about 10% to about 40%.

The solvent component is preferably present in an amount of from about20% to about 90% by weight of the overall blend. A more preferred rangeis from about 30% to about 70% and most preferably from about 40% toabout 60%. The greater the percentage of high volatility solventemployed, the thinner is the resulting film. The greater the percentageof low volatility solvent employed, the greater is the resultingporosity

The mole ratio of water to the silane component is preferably from about0 to about 50. A more preferred range is from about 0.1 to about 10 andmost preferably from about 0.5 to about 1.5. The acid is present in acatalytic amount which can be readily determined by those skilled in theart. Preferably the molar ratio of acid to silane ranges from about 0 toabout 0.2, more preferably from about 0.001 to about 0.05, and mostpreferably from about 0.005 to about 0.02.

The prepared silicon-based dielectric precursor is then coated on asubstrate. The layer is relatively uniformly applied. While thesubstrate can be any art-known material, e.g., as described supra,typical substrates are polished semiconductor wafers, optionally havingone or more semiconductor components previously fabricated on thesurface.

The solvent, usually the higher volatility solvent is then at leastpartially evaporated from the coating. The more volatile solventevaporates over a period of seconds or minutes. At this point, the filmis a viscous liquid of the silica precursors and the less volatilesolvent. Slightly elevated temperatures may optionally be employed toaccelerate this step. Such temperatures may range from about 20° C. toabout 80° C., preferably range from about 20° C. to about 50° C. andmore range from about 20° C. to about 35° C.

The coated substrate is then placed in a sealed chamber and is rapidlyevacuated to a vacuum. In the preferred embodiment, the pressure of theevacuated chamber ranges from about 0.001 torr to about 0.1 torr, orgreater. In an alternative embodiment, the chamber pressure may rangefrom about 0.001 torr to about 760 torr, or greater. Typically, thepressure is about 250 torr. Then the coating is sequentially exposed toboth a water vapor and a base vapor, either simultaneously orsequentially. For purposes of this invention, a base vapor includesgaseous bases. Preferably the coating is first exposed to a water vaporand then exposed to a base vapor, however, in an alternate embodiment,the coating may first be exposed to a base vapor and then a water vapor.The first of the two exposures is conducted such that thereafter thepressure in the chamber remains at sub-atmospheric pressure. The secondexposure may be conducted at atmospheric pressure, sub-atmosphericpressure or super-atmospheric pressure.

In one preferred embodiment, after the coated substrate is placed in thesealed chamber and the chamber evacuated to a vacuum, a valve is openedto a reservoir of water, and water vapor quickly fills the chamber. Thepartial pressure of water vapor, P_(H2O) is controlled by the length oftime that the valve is open and the temperature at which the liquidwater reservoir is maintained. Because of the low vapor pressure ofwater, the chamber pressure after water addition is much less thanambient. The pressure rise that occurs in the chamber during the watervapor addition is a direct measure of the water vapor partial pressure.In the preferred embodiment, the pressure of the evacuated chamber afterthe water vapor exposure ranges from about 0.1 torr to about 150 torr,preferably about 1 torr to about 40 torr and more preferably from about5 torr to about 20 torr. In the preferred embodiment, the temperature ofthe water during the exposure ranges from about 10° C. to about 60° C.,preferably from about 15° C. to about 50° C., and more preferably fromabout 20° C. to about 40° C. In the preferred embodiment, thetemperature in the chamber after water exposure ranges from about 10° C.to about 50° C., preferably from about 15° C. to about 40° C., and morepreferably from about 20° C. to about 40° C.

After water vapor addition, a base vapor is dosed into the chamber. Thechamber pressure after base dosing may be at, above or below atmosphericpressure. If the pressure is above atmospheric, the chamber must bedesigned to resist the total system pressure. As with water vapor, thepartial pressure of the base is known directly from the pressure riseduring base dosing. Because the chamber only contains base and watervapor, except for trace amounts of atmospheric gas left from the initialchamber pumpdown, the base and water diffusion rates are much fasterthan the case when evacuation is not conducted, resulting in greatlyincreased polymerization rates, decreased process time per coatedsubstrate, and greater uniformity across the coated surface. Since thebase and water vapor are added separately, their partial pressures areeasily measured and there is very little waste. Only the vapor above thewafer need be removed upon deposition. The order of addition of waterand base may be reversed but the addition of water before the base ispreferred because of its lower vapor pressure. In the preferredembodiment, the pressure of the evacuated chamber after the base vaporexposure ranges from about 100 torr to about 2,000 torr, preferablyabout 400 torr to about 1,000 torr and more preferably from about 600torr to about 800 torr. In the preferred embodiment, the temperature ofthe base during the exposure ranges from about 10° C. to about 60° C.,preferably from about 15° C. to about 40° C., and more preferably fromabout 20° C. to about 30° C. In the preferred embodiment, thetemperature in the chamber after base exposure ranges from about 10° C.to about 50° C., preferably from about 15° C. to about 40° C., and morepreferably from about 20° C. to about 40° C.

Suitable bases (i.e., alkaline regents) for use in the base vapornonexclusively include ammonia and non-volatile amines, such as primary,secondary and tertiary alkyl amines, aryl amines, alcohol amines andmixtures thereof which have a boiling point of about 200° C. or less,preferably 100° C. or less and more preferably 25° C. or less. Preferredamines do not require an atmosphere for aging, i.e., while the film isbeing impressed with a flat surface, and include, for example,monoethanol amine, tetraethylenepentamine, 2-(aminoethylamino)ethanol,3-aminopropyltriethoxy silane, 3-amino-1,2-propanediol,3-(diethylamino)-1,2-propanediol,n-(2-aminoethyl)-3-aminopropyl-trimethoxy silane,3-aminopropyl-trimethoxy silane. Additional amines that are useful forthe processes of the invention include, e.g., methylamine,dimethylamine, trimethylamine, n-butylamine, n-propylamine, tetramethylammonium hydroxide, piperidine and 2-methoxyethylamine. The ability ofan amine to accept a proton in water is measured in terms of the basicconstant K_(b), and pK_(b)=−log K_(b). In the preferred embodiment, thepK_(b) of the base may range from about less than 0 to about 9. A morepreferred range is from about 2 to about 6 and most preferably fromabout 4 to about 5.

Preferably, the mole ratio of water vapor to base vapor ranges fromabout 1:3 to about 1:100, preferably from about 1:5 to about 1:50, andmore preferably from about 1:10 to about 1:30.

The water vapor causes a continued hydrolysis of the alkoxysilane alkoxygroups, and the base catalyzes condensation of the hydrolyzedalkoxysilane and serves to increase molecular weight until the coatinggels and ultimately increases gel strength. The film is then dried in aconventional way by solvent evaporation of the less volatile solvent.Elevated temperatures may be employed to dry the coating in this step.Such temperatures may range from about 20° C. to about 450° C.,preferably from about 50° C. to about 350° C. and more preferably fromabout 175° C. to about 320° C.

Optionally, additional process steps may be applied to the formednanoporous silica dielectric film, including, for example, a solventrinse, a surface modification to enhance hydrophobicity, and any otherart-known process steps as required.

After the desired time of reaction after base addition, on the order ofseconds to a few minutes, the chamber pressure is brought to atmosphericpressure. This can be accomplished by either adding an inert gas such asnitrogen and opening the chamber or evacuating the base/water mixturevia vacuum and backfilling with an inert gas, or even optionally ventingthe chamber with a non-inert gas, such as air.

Thus, a precursor is deposited on a wafer and the more volatile solventcontinues to evaporate over a period of seconds. The wafer is placed ina sealed chamber at ambient pressure. The chamber is opened to a vacuumsource and the ambient gas is evacuated and the chamber pressuredecreases well below the partial pressure of water vapor. In the nextstep, water vapor is added and the chamber pressure increases. Thepressure increase during that step is the water partial pressure(P_(H2O)). The base vapor, in this case ammonia, is introduced into thechamber and polymerization is triggered. The pressure increase duringthis step is the base partial pressure (for example, P_(NH3)), so thatthe total pressure in the chamber at the end of the ammonia additioncycle is the sum of the partial pressures of water vapor and ammonia.After the desired time, the chamber pressure may be raised to ambient byfilling with an inert gas, such as nitrogen as shown, or it may be firstevacuated to vacuum and subsequently backfilled to ambient pressure.

As a result, a relatively high porosity, low dielectric constant,silicon containing polymer composition forms on the substrate surface.The silicon containing polymer composition preferably has a dielectricconstant of from about 1.1 to about 3.5, more preferably from about 1.3to about 3.0, and most preferably from about 1.5 to about 2.5. The poresize of silica composition ranges from about 1 nm to about 100 nm, morepreferably from about 2 nm to about 30 nm, and most preferably fromabout 3 nm to about 20 nm. The density of the silicon containingcomposition, including the pores, ranges from about 0.1 to about 1.9g/cm², more preferably from about 0.25 to about 1.6 g/cm², and mostpreferably from about 0.4 to about 1.2 g/cm².

B. Methods of Producing Dielectric Film By Applying Base Material Mixedin Mid-Stream

In another preferred embodiment, the nanoporous silica dielectric filmis prepared by coating a substrate with a silicon-based precursorcomposition that is pre-mixed by combining multiple streams offree-flowing component precursor reagents before the composition isapplied to a substrate. In this embodiment, a nanoporous silicadielectric film is formed on a substrate by

(i) combining a stream of a silicon-based precursor or base material,such as, for example, an alkoxysilane composition, with a stream of abase containing catalyst composition to form a combined compositionstream; immediately depositing the combined composition stream onto asurface of a substrate and exposing the combined composition to water(in either order or simultaneously); and planarizing the film during thecuring of the combined composition; or

(ii) combining a stream of a silicon-based precursor or base material,such as, for example, an alkoxysilane composition, with a stream ofwater to form a combined composition stream; immediately depositing thecombined composition stream onto a surface of a substrate; andplanarizing the film during the curing of the combined composition.

Methods (i) and (ii) are described in detail, absent the planarizationfeatures of the present invention, in co-owned U.S. application Ser. No.09/140,855, filed on Aug. 27, 1998, the disclosure of which isincorporated by reference herein in its entirety. Processes for thepreparation of nanoporous dielectric silica films by mixing streams ofcomponents is summarized in greater detail, as follows. Modifications tomethods described in U.S. application Ser. No. 09/140,855 are thoseoptionally required by the need for contacting the film material with aplanarization object.

The first step of this process is to prepare a base material in the formof a mixture of at least one precursor, such as an alkoxysilane, asdescribed for Formula I, supra, and a solvent composition. The mixtureis then discharged onto a suitable substrate in the form of a stream. Inone preferred embodiment, the stream of alkoxysilane composition iscombined with a stream of water to form a combined composition streamimmediately prior to contacting the substrate.

In an alternate preferred embodiment, a combined composition stream isformed from a stream of the alkoxysilane composition and a stream of abase (i.e. alkaline) containing catalyst composition, e.g., an aminecompound, as described, supra. The combined composition stream isthereafter deposited onto a surface of a substrate. Optionally, thecombined composition stream is deposited onto the substrate and is thenexposed to the water, in the form of a water vapor atmosphere.Alternatively, the combined composition stream is exposed to the waterbefore deposition onto the substrate. In yet another option, thecombined composition stream is simultaneously exposed to the water anddeposited onto the substrate. This may be in the form of a water streamor a water vapor atmosphere. After deposition and water exposure, thecombined composition may be cured, aged, or dried before, during orafter planarization, to thereby form a nanoporous dielectric coating onthe substrate.

Whichever of the above options is selected for conducting the process,the above-described components of the combined stream compositioncontact each other in the space above the surface of the substrate,immediately prior to deposition. At a point of confluence of theindividual streams, the combined stream is unbounded by tubing, piping,manifolds or the like. This minimizes reaction time between thecomponents prior to deposition and prevents reaction within theintersection point of supply tubes.

Preferably, the components are all in a liquid form and any suitableapparatus for distributing the liquid components may be used fordepositing the above-described combined streams of, e.g., alkoxysilane,water and base compositions according to the present invention. Suitableapparatus includes, for example, syringe pumps, but the artisan willappreciate that other devices may be used to form the combinedcomposition stream. Such nonexclusively include faucets, sprayers,hoses, tanks, pipes, tubes, and the like. Various methods of combiningthe components may be used, such as dripping, squirting, streaming,spraying, and the like.

Exemplary apparatus for conducting this process includes separatecontainers, e.g., tanks, for storing separate components until theprocess begins. Each respective tank has a corresponding separatedischarge tube for discharging the respective component to be combinedinto a single stream, so that the combined stream can be deposited ontoa substrate surface. Each component is propelled through its respectivedischarge tube by, e.g., gravity feed and/or by the action of one ormore pumps. The artisan will also appreciate that the apparatus can alsoprovide for propelling one or more component(s) by applying positive gasor air pressure to the corresponding storage tank. The flow through eachrespective discharge tube is optionally regulated by one or more flowcontrol valves located between the distal end of each discharge tube andits respective tank and/or by control of the pumping action, when pumpsare employed to propel flow of components. If the components arepropelled by air or gas pressure, component flow can also be regulated,in whole or in part, by controlling the pressure of the air or gaspropellant.

The discharge tubes are positioned so that each of the respectivedischarge streams combine together to form a combined compositionstream, which is deposited onto a surface of a substrate positioned toreceived the combined composition stream. Optionally, each dischargetube may also include a shaped nozzle, e.g., a spinner nozzle, or anozzle formed of one or more openings, e.g., analogous to a showerhead,suitable for forming a discharge stream that mixes well with other suchstreams. The artisan will appreciate that the dimensions of any providednozzle, and/or the discharge end of each discharge tube, can be readilymodified to assist in regulating pressure and flow rate for each stream,to assure optimal stream contact, mixing, and spreading of the resultingmixed composition stream over the substrate, depending, for example,upon the rate at which the process is conducted, the reaction speed, andthe viscosity of the respective component.

A variety of processes may be employed by this method to form ananoporous dielectric film on a substrate. For a two-component processthe components can be, for example, alkoxysilane composition and water,each stored in a separate tank until needed, or alternatively, a basecontaining catalyst composition in place of the water component.

For a three-component process, the apparatus can have three separatetanks each with a corresponding discharge tube for discharging one ofthree components, e.g., an alkoxysilane composition, a base containingcatalyst composition, and water, respectively. Additional storage tanksand discharge tubes can be added, if required to deliver additionalcomponent(s) for the selected process.

The above-described apparatus can also be modified so that a combinedstream is deposited onto a substrate in a closed environment which holdsat least one additional component in vapor form. For example, when thecombined stream is formed of alkoxysilane and base catalyst, thecombined stream can be deposited on a substrate positioned in a closedenvironment that includes a water vapor atmosphere. The closedenvironment can be formed by any suitable chamber or enclosure able tocontain the substrate and vapor component(s). The enclosure will have aninlet or inlets for the component discharge tubes. Preferably, theenclosure portion of the apparatus will also include an additionalinlet, with an optional valve, to admit a vapor, a gas-vapor mixture oroptionally a liquid to be converted to vapor within the enclosure.

For example, with a two-component combined stream as described above,the apparatus will be constructed as broadly described above, with theadditional components of a source of water vapor, e.g., an evaporationbottle or chamber, the evaporation bottle preferably including a heatsource for promoting water vaporization and optionally a source offlowing air or inert gas to carry the water vapor into the enclosure.With the enclosure of the substrate, this apparatus operates to exposethe combined composition stream to water either during or afterdeposition onto a surface of the enclosed substrate. The enclosure willalso optionally include outlets to allow for venting and/or recycling ofthe unreacted water vapor and/or other unreacted components.

Useful alkoxysilanes include those defined as for Formula I, supra. Alsoas defined supra, preferred alkoxysilanes nonexclusively includetetraethoxysilane (TEOS) and tetramethoxysilane.

The solvent composition for the base component, e.g., an alkoxysilane,preferably comprises a relatively high volatility solvent or arelatively low volatility solvent or both a relatively high volatilitysolvent and a relatively low volatility solvent. The solvent, usuallythe higher volatility solvent, is at least partially evaporatedimmediately after deposition onto the substrate. This partial dryingleads to better planarity, even absent the additional planarizationsteps of the instant invention, due to the lower viscosity of thematerial after the first solvent or parts of the solvent comes off. Themore volatile solvent evaporates over a period of seconds or minutes.Slightly elevated temperatures may optionally be employed to acceleratethis step. Such temperatures preferably range from about 20° C. to about80° C., more preferably from about 20° C. to about 50° C. and mostpreferably from about 20° C. to about 35° C.

The meaning of the expressions, “a relatively high volatility solvent”and “a relatively low volatility solvent composition” is as defined inSection A, supra.

The alkoxysilane component is preferably present in an amount of fromabout 3% to about 50% by weight of the overall blend, more preferablyfrom about 5% to about 45% and most preferably from about 10% to about40%.

The solvent component of the alkoxysilane precursor composition ispreferably present in an amount of from about 20% to about 90% by weightof the overall blend, more preferably from about 30% to about 70% andmost preferably from about 40% to about 60%. When both a high and a lowvolatility solvent are present, the high volatility solvent component ispreferably present in an amount of from about 20% to about 90% by weightof the overall blend, more preferably from about 30% to about 70% and amost preferably from about 40% to about 60% by weight of the overallblend. When both a high and a low volatility solvent are present, thelow volatility solvent component is preferably present in an amount offrom about 1 to about 40% by weight of the overall blend, morepreferably from about 3% to about 30% and a most preferably from about5% to about 20% by weight of the overall blend.

Typical substrates are those suitable to be processed into an integratedcircuit or other microelectronic device as described in detail, supra.

The base containing catalyst composition contains a base, or a base pluswater, or a base plus an organic solvent, or a base plus both water andan organic solvent. The base is present in a catalytic amount which canbe readily determined by those skilled in the art. Preferably the molarratio of base to silane ranges from about 0 to about 0.2, morepreferably from about 0.001 to about 0.05, and most preferably fromabout 0.005 to about 0.02. Water is included to provide a medium forhydrolyzing the alkoxysilane. The mole ratio of water to silane ispreferably from about 0 to about 50, more preferably from about 0.1 toabout 10 and a most preferably from about 0.5 to about 1.5. Suitablesolvents for the base containing catalyst composition include thoselisted above as a high volatility solvent. Most preferred solvents arealcohols such as ethanol and isopropanol.

The temperature of the water during the exposure preferably ranges fromabout 10° C. to about 60° C., more preferably from about 15° C. to about50° C., and most preferably from about 20° C. to about 40° C. Thetemperature of the base during the exposure preferably ranges from about110° C. to about 60° C., more preferably from about 15° C. to about 40°C., and most preferably from about 20° C. to about 30° C.

Suitable bases nonexclusively include ammonia and amines, such asprimary, secondary and tertiary alkyl amines, aryl amines, alcoholamines and mixtures thereof which have a preferred boiling point of atleast about −50° C., more preferably at least about 50° C., and mostpreferably at least about 150° C. Suitable amines, in addition to thoserecited supra, also include, alcoholamines, alkylamines, methylamine,dimethylamine, trimethylamine, n-butylamine, n-propylamine, tetramethylammonium hydroxide, piperidine, 2-methoxyethylamine, mono-, di- ortriethanolamines, and mono-, di-, or triisopropanolamines.

The combined composition may be cured, aged, or dried in a conventionalway such as solvent evaporation of the less volatile solvent. Elevatedtemperatures may be employed to cure, age or dry the coating. Suchtemperatures preferably range from about 20° C. to about 450° C., morepreferably from about 50° C. to about 350° C. and most preferably fromabout 175° C. to about 320° C.

As a result, a relatively high porosity, low dielectric constant siliconcontaining polymer composition is formed on the substrate. The siliconcontaining polymer composition preferably has a dielectric constant offrom about 1.1 to about 3.5, more preferably from about 1.3 to about3.0, and most preferably from about 1.5 to about 2.5. The pore size ofsilica composition preferably ranges from about 1 nm to about 100 nm,more preferably from about 2 nm to about 30 nm, and most preferably fromabout 3 nm to about 20 nm. The density of the silicon containingcomposition, including the pores, preferably ranges from about 0.1 toabout 1.9 g/cm², more preferably from about 0.25 to about 1.6 g/cm², andmost preferably from about 0.4 to about 1.2 g/cm².

C. Variations on Film Forming Processes

Variations on and modifications to the above-described processes forfabricating a nanoporous silica dielectric film have been described in anumber of co-owned U.S. patent applications and may optionally beutilized in the practice of the instant invention.

For example, the above-described methods may be modified by producing afilm with at least two-different regions of density, i.e., adjacentregions of relatively high and relatively lower density. This isaccomplished by blending at least one alkoxysilane with a relativelyhigh volatility solvent composition, a relatively low volatility solventcomposition and optional water, thus forming a mixture, and causing apartial hydrolysis and partial condensation of the alkoxysilane;depositing the mixture onto a suitable substrate, while evaporating atleast a portion of the relatively high volatility solvent composition;exposing the mixture to a water vapor and a base vapor; and evaporatingthe relatively low volatility solvent composition. Optionally, themixture of alkoxysilane and solvents can include catalytic amounts of anacid to produce a pH of, e.g., about 2 to about 5. Further details aredisclosed by co-owned U.S. application Ser. Nos. 09/046,473 and09/046,475, both filed on Mar. 25, 1998, the disclosures of which areincorporated by reference herein in their entireties.

In a second variation, water and base vapor mixing efficiencies areimproved by blending at least one alkoxysilane with a solventcomposition and optional water and applying the blend to a semiconductorsubstrate. The substrate is then placed in a sealed chamber that is thenevacuated to a pressure below atmospheric pressure. The substrate isthen sequentially exposed to water vapor and a base vapor, in eitherorder, at a pressure below atmospheric pressure. Further details aredisclosed by U.S. co-owned Ser. No. 09/054,262, filed on Apr. 3, 1998,the disclosure of which is incorporated by reference herein in itsentirety.

In a third variation, precursors of an alkoxysilane are employed to formnanoporous dielectric films on a substrate. The dielectric films isformed by applying a precursor mixture to a substrate. The precursormixture is formed of the following components: a relatively lowvolatility solvent composition that includes a C₁ to C₄ alkylether of aC₁ to C₄ alkylene glycol which is miscible in water and alkoxysilanes.The low volatility solvent composition also has relatively low hydroxylconcentration (e.g, of 0.0084 mole/cm³ or less, or 0.021 mole/cm³, orless), a boiling point of about 175° C. or more at atmospheric pressure,and an average molecular weight ranging from about 100 to about 120, ormore. The precursor mixture also includes a relatively high volatilitysolvent composition having a boiling point below that of the relativelylow volatility solvent composition; optional water and an optionalcatalytic amount of an acid. Further details are provided by co-ownedU.S. application Ser. Nos. 09/111,081, 09/111,082, both filed on Jul. 7,1998, the disclosures of which are incorporated by reference herein intheir entireties.

In a fourth variation, precursors of an alkoxysilane are employed toform nanoporous dielectric films on a substrate by vapor deposition,employing silica precursors suitable for vapor deposition as definedabove, by Formula I and the associated enumeration of preferred silicaspecies. The silica precursor, with an optional co-solvent, is depositedon a substrate from the vapor phase to form a liquid-like film.Polymerization/gelation are initiated, e.g., generally as previouslydescribed, followed by drying the polymerized nanoporous dielectricfilm. Further details are provided by co-owned U.S. application Ser. No.09/111,083, filed on Jul. 7, 1998, the disclosure of which isincorporated by reference herein in its entirety.

In a fifth variation, a uniform nanoporous dielectric film can be formedon a horizontally positioned flat substrate centered and held within acup having an open top section and a removable cover for closing thetop. A liquid alkoxysilane composition is deposited onto the substratesurface; covering the cup such that the substrate is enclosed therein;spinning the covered cup and spreading the alkoxysilane compositionevenly on the substrate surface. The alkoxysilane composition is thenexposed to water vapor and base vapor, injected, e.g., through a vaporinjection port that extends through the center of the cover. Contactwith the injected vapor(s) forms a gel which is then cured. Furtherdetails are provided by co-owned U.S. application serial No. 60/095,573,filed on Aug. 6, 1998, the disclosure of which is incorporated byreference herein in its entirety.

In a sixth variation, nanoporous silica dielectric coatings are formedon a substrate via partial evaporation of a relatively low volatilitysolvent. A precursor composition is formed from an alkoxysilane, anacid, and a solvent composition containing a high volatility and lowvolatility solvent. The precursor composition is optionally combinedwith base catalyst and/or water prior to or after depositing theprecursor composition onto a substrate. The relatively high volatilitysolvent is evaporated, and the low volatility solvent is partiallyevaporated from the precursor composition. Further details are providedby co-owned U.S. application Ser. No. 09/234,609, filed on Jan. 21,1999, the disclosure of which is incorporated by reference herein in itsentirety.

In a seventh variation, a suitable substrate that includes a dielectricfilm is treated in a substantially oxygen free environment by heatingthe substrate to a temperature of about 350° C. or greater, for a timeperiod of at least about 30 seconds. Further details are provided byco-owned U.S. application serial No. 60/098,515, filed on Aug. 31, 1998,the disclosure of which is incorporated by reference herein in itsentirety.

In an eighth variation, a substantially uniform alkoxysilane gelcomposition is formed on a surface of a substrate. The alkoxysilane gelcomposition includes a combination of at least one alkoxysilane, anorganic solvent composition, water, and an optional base catalyst. Thesubstrate is heated for a sufficient time and at a sufficienttemperature in an organic solvent vapor atmosphere to condense the gelcomposition; and then the gel composition is cured to form a nanoporousdielectric coating having high mechanical strength, on the substrate.Further details are provided by co-owned U.S. application Ser. No.09/141,287, filed on Aug. 27, 1998, the disclosure of which isincorporated by reference herein in its entirety.

In a ninth variation, nanoporous silica dielectric coatings are formedon a substrate via chemical vapor deposition. Simply by way of example,at least one alkoxysilane composition is vaporized and the vaporizedalkoxysilane composition is deposited onto a substrate. The depositedprecursor is then exposed to a gelling agent, e.g., water vapor, andeither an acid or a base vapor; and dried to form a relatively highporosity, low dielectric constant, silicon containing polymercomposition on the substrate. Further details are provided by co-ownedU.S. application Ser. No. 09/111,083, filed on Jul. 7, 1998, thedisclosure of which is incorporated by reference herein in its entirety.

D. Surface Modification Reagents and Methods

Typically, the silica-based materials, such as the alkoxysiloxanesmentioned herein, form nanoporous films with surfaces, includingsurfaces of the pore structures, that contain silanol groups. Silanolsand the water that they can adsorb from the air are highly polarizablein an electric field, and thus will raise the dielectric constant of thefilm. To make nanoporous films substantially free of silanols and water,an organic reagent, i.e., a surface modification agent, such ashexamethyldisilazane or methyltriacetoxysilane, is optionally introducedinto the pores of the film. Such silylation reagent react with silanolson the pore surfaces to add organic, hydrophobic capping groups, e.g.,trimethylsilyl groups. Thus, it has been found desirable to conductadditional processing steps to silylate free surface silanol groups, orto employ multifunctional base materials, as described supra, which donot produce such surface silanol groups.

A number of surface modification agents and methods for producinghydrophobic, low dielectric nanoporous silica films have been described,for example, in co-owned U.S. application Ser. Nos. 60/098,068 and09/140,855, both filed on Aug. 27, 1998, 09/234,609 and 09/235,186, bothfiled on Jan. 21, 1999, the disclosures of which are incorporated byreference herein in their entirety.

One preferred surface modification agent is a compound having a formulaselected from the group consisting of Formulas IV (1)-(7):

(1) R₃SiNHSiR₃, (2) R_(x)SiCl_(y), (3) R_(x)Si(OH)_(y), (4) R₃SiOSiR₃,

(5) R_(x)Si(OR)_(y), (6) M_(p)Si(OH)_([4-p]), and/or (7)R_(x)Si(OCOCH₃)_(y)

and combinations thereof, wherein x is an integer ranging from 1 to 3, yis an integer ranging from 1 to 3 such that y=4−x, p is an integerranging from 2 to 3; each R is an independently selected from hydrogenand a hydrophobic organic moiety; each M is an independently selectedhydrophobic organic moiety; and R and M can be the same or different.The R and M groups are preferably independently selected from the groupof organic moieties consisting of alkyl, aryl and combinations thereof.The alkyl moiety is substituted or unsubstituted and is selected fromthe group consisting of straight alkyl, branched alkyl, cyclic alkyl andcombinations thereof, and wherein said alkyl moiety ranges in size fromC₁ to about C₁₈. The aryl moiety is substituted or unsubstituted andranges in size from C₅ to about C₁₈. Preferably the surface modificationagent is selected from the group consisting of acetoxytrimethylsilane,acetoxysilane, diacetoxydimethylsilane, methyltriacetoxysilane,phenyltriacetoxysilane, diphenyldiacetoxysilane, trimethylethoxysilane,trimethylmethoxysilane, 2-trimethylsiloxypent-2-ene-4-one,n-(trimethylsilyl)acetamide, 2-(trimethylsilyl) acetic acid,n-(trimethylsilyl)imidazole, trimethylsilylpropiolate,trimethylsilyl(trimethylsiloxy)-acetate, nonamethyltrisilazane,hexamethyldisilazane, hexamethyldisiloxane, trimethylsilanol,triethylsilanol, triphenylsilanol, t-butyldimethylsilanol,diphenylsilanediol and combinations thereof. Most preferably the surfacemodification agent is hexamethyldisilazane. The surface modificationagent may be mixed with a suitable solvent such as acetone, applied tothe nanoporous silica surface in the form of a vapor or liquid, and thendried.

Additional surface modification agents include multifunctional surfacemodification agents as described in detail in co-owned U.S. Ser. No.09/235,186, incorporated by reference herein in its entirety, asdescribed above. Such multifunctional surface modification agents can beapplied in either vapor or liquid form, optionally with or withoutco-solvents. Suitable co-solvents include, e.g., ketones, such asacetone, diisolpropylketon, and others, as described in detail inco-owned U.S. application Ser. No. 09/111,084, filed on Jul. 7, 1998,the disclosure of which in incorporated by reference herein in itsentirety. For example, as described in detail in U.S. Ser. No.09/235,186, as incorporated by reference above, certain preferredsurface modification agents will have two or more functional groups andreact with surface silanol functional groups while minimizing masspresent outside the structural framework of the film, and include, e.g.,suitable silanols such as

R₁Si(OR₂)₃  Formula V

wherein R₁ and R₂ are independently selected moieties, such as H and/oran organic moiety such as an alkyl, aryl or derivatives of these. WhenR₁ or R₂ is an alkyl, the alkyl moiety is optionally substituted orunsubstituted, and may be straight, branched or cyclic, and preferablyranges in size from C₁ to about C₁₈, or greater, and more preferablyfrom C₁ to about C₈. When R₁ or R₂ is aryl, the aryl moiety preferablyconsists of a single aromatic ring that is optionally substituted orunsubstituted, and ranges in size from C₅ to about C₁₈, or greater, andmore preferably from C₅ to about C₈. In a further option, the arylmoiety is not a heteroaryl.

Thus, R₁ or R₂ are independently selected from H, methyl, ethyl, propyl,phenyl, and/or derivatives thereof, provided that at least one of R₁ orR₂ is organic. In one embodiment, both R₁ and R₂ are methyl, and atrifunctional surface modification agent according to Formula V ismethyltrimethoxysilane.

In another embodiment, a suitable silane according to the invention hasthe general formula of

R₁Si(NR₂R₃)₃  Formula VI

Wherein R₁, R₂, R₃ are independently H, alkyl and/or aryl. When any ofR₁, R₂, R₃ are alkyl and/or aryl, they are defined as for Formula V,above. In preferred embodiments according to Formula VI, R₁ is selectedfrom H, CH₃, C₆H₅, and R₂ and R₃ are both CH₃. Thus trifunctionalsurface modification agents according to Formula VI include, e.g.,tris(dimethylamino)methylsilane, tris(dimethylamino)phenylsilane, and/ortris(dimethylamino)silane.

In yet another embodiment, a suitable silane according to the inventionhas the general formula of

R₁Si(ON═CR₂R₃)₃  Formula VII

wherein R₁, R₂, R₃ are independently H, alkyl and/or aryl. When any ofR₁, R₂, R₃ are alkyl and/or aryl, they are defined as for Formula VII,above. In one preferred embodiment, R₁ and R₂ are both CH₃, and R₃ isCH₂CH₃. Thus trifunctional surface modification agents according toFormula VII include, e.g., methyltris(methylethylkeoxime)silane.

In yet a further embodiment, a suitable silane according to theinvention has the general formula of

R₁SiCl₃  Formula VIII

wherein R₁ is H, alkyl or aryl. When R₁ is alkyl and/or aryl, they aredefined as for Formula IV, above. In one preferred embodiment, R₁ isCH₃. Thus trifunctional surface modification agents according to FormulaVIII include, e.g., methyltrichlorosilane.

In a more preferred embodiment, the capping reagent includes one or moreorganoacetoxysilanes which have the following general formula,

(R₁)Si(OCOR₂)_(y)  Formula IX

Preferably, x is an integer ranging in value from 1 to 2, and x and ycan be the same or different and y is an integer ranging from about 2 toabout 3, or greater.

Useful organoacetoxysilanes, including multifunctionalalkylacetoxysilane and/or arylacetoxysilane compounds, include, simplyby way of example and without limitation, methyltriacetoxysilane(“MTAS”), dimethyldiacetoxysilane (DMDAS), phenyltriacetoxysilane anddiphenyldiacetoxysilane and combinations thereof.

In an alternative embodiment, surface modification is provided byannealing the film with an electron beam. After a base material isdeposited on a substrate, and optionally heated to evaporate solvents,the deposited composition is then annealed by exposure to electron beamradiation, in vacuo, at a temperature ranging from about 25° C. to about1050° C., with a beam energy ranging from about 0.5 to about 30 KeV andan energy dose ranging from about 500 to about 100,000 μC/cm²,respectively. The resulting films have essentially no or a reducedamount of carbon and hydrogen after the electron beam process. Withmethyl groups driven out of the nanoporous silica film, the hydrophobicand polarizable trimethylsilanols are reduced or not present. Furtherdetails are provided by co-owned U.S. application Ser. No. 09/227,734,filed on filed on Jan. 9, 1999.

E. Contact Planarization Methods

Broadly, production of planarized nanoporous dielectric silica filmcoatings on substrates can be conducted by applying a prepared liquid orvapor composition, that includes a suitable silicon-based dielectricprecursor, to a substrate, and then completing formation of the desirednanoporous silica dielectric film, by methods modified to includecontact with a planarization object, as follows.

(a) Increasing the coating viscosity by aging, Le., gelling, by means ofa pre-added non-volatile acid or base catalyst and/or water, or bycontacting the coating with an acid or base catalyst and/or water afterapplication to the substrate.

(b) Contacting the coating with an i.e., a planarization object, havingat least one contact surface able to impart the desired degree ofplanarity, with sufficient pressure to transfer a planar impression tothe coating without substantially impairing formation of nanoporousstructure.

(c) Separating the planarized coating from the planarizing object.

(d) Curing the surface to hardness.

It will be appreciated that these steps can be readily conducted in theorder listed above or in a different order, as illustrated by Table 1.

TABLE 1 Order of Steps (after coating substrate) Description (a), (b),(c) Age; contact planarization object; and (d) separate from object; andthen cure. (a), (d), (b) Age; cure; contact planarization object; andthen and (c) separate from object. (b), (a), (d) Contact planarizationobject; allow aging to continue; and (c) cure; separate from object.(with application of e.g., S.O.G. composition pre-mixed/treated withgelling agent and, curing in the press). (b), (c), (a) Contactplanarization object; separate from object; allow and (d) aging tocontinue; cure (with application of e.g., S.O.G. composition pre-mixedor pre-treated with gelling agent).

In one option, a fluid that includes a silicon-based dielectricprecursor also includes viscosity enhancers to permit contact with aplanarization object and/or a removable, non-stick film, beforesignificant viscosity enhancement by the aging process has taken place.

In another option, a protective liner and/or additional protectivecoating, e.g., is applied onto the substrate surface, prior toapplication of the silica dielectric precursor(s). The substrate can beany potential or partially fabricated semiconductor device, or othertype of device, as described supra.

At an appropriate processing stage after the substrate is coated, whilethe coating remains plastic and able to be impressed with a flat surfacewhile retaining the capacity to form a desired nanoporous structure, thecoated substrate is transferred to a press machine, a roller machine,and/or any other art-known device for impressing a flat surface onto thefilm-coated substrate. There, a planarization object, i.e., an objecthaving at least one surface having the necessary capacity to impress aplanar surface on the coating, such as an optical flat, is contacted,preferably under pressure, with the coating on the substrate.

Preferably, as mentioned supra, a release layer, such as a non-stickfluorocarbon surface or other art-known material of similar properties,is positioned between the planarization object contact surface and thecoating to be planarized. For convenience, the non-stick releasematerial can be a non-stick film that can be separately applied andseparately removed from the planar object contact surface and theplanarized coating. In addition, if the substrate is only being coatedon one side at a time, a protective layer of a soft material is placedunder the other side of the substrate to protect it from damage.

It will also be appreciated that the pressure and duration of theplanarization step will vary, depending on the properties of thedielectric coating, including the type of precursor material, viscosityof the coating, coating thickness and the degree of aging and/or curing,if any, that has taken place at the start of the pressing.

In a preferred aspect of the invention, the applied pressure ranges fromabout 0.1 MPa to about 1 GPa. More preferably, the applied pressureranges from about 0.2 MPa to about 10 MPa (pressure units in Pascals).The duration of the pressing step preferably ranges from about 10 sec toabout 30 minutes, and more preferably, from about 30 sec to about 10minutes.

In a further aspect of the invention, the coating to be planarized canbe exposed to vacuum prior to pressing to speed removal of vapors and/ordissolved gases in order to minimize undesirable bubble formation.Alternatively, the pressing step can be conducted in vacuum. Optionally,the film can be heated and cured while still under pressure in the pressor after removal from the press.

The following nonlimiting examples serve to illustrate the invention.

EXAMPLE 1

This example illustrates a process wherein a precursor is mixed with anaging agent, the mixture was then spin deposited onto a surface of asilicon wafer having a pattern of metal wiring on that surface. Thecoated wafer was then placed in a press with an optical flat having arelease layer in contact with the coating.

The base materials, including a dielectric precursor and an aging agent,were mixed for 30 sec before the substrate was spin coated onto testwafers of 4 and 6 inches in diameter. The films were spun on a Solitec™machine (Solitec Wafer Processing, Inc., San Jose, Calif.) using manualdispense with a spin speed that ranged from 1000 to 4000 rpm. Theprecursor was a partially hydrolyzed and partially condensed fluidalkoxysilane composition (available from AlliedSignal Corp., AdvancedMicroelectronic Materials Sunnyvale, Calif. as Nanoglass® K2.2),prepared with 21.6% EtOH mixed with 8.75% monoethanolamine (“MEA”) inEtOH. MEA is a nonvolatile base aging agent. The ratio of precursor tothe base ranges from about 1:0.34 to about 1:0.26.

The Process can be Summarized as Follows:

1) mix Nanoglass precursor with MEA (defined as time 0).

2) deposit and spin film onto silicon wafer.

3) put wafer into press and apply Teflon™ sheet (90 to 210s after time0).

4) leave in press for 10 min.

5) return to spin coater, perform solvent exchange usingHMDZ/3-pentanone, spin dry.

6) hot plate bake at 175° C. and 320° C. for 1 min each.

7) furnace cure at 400° C. for 30 min.

After mixing (time zero), a flat Teflon™ sheet was applied onto thecoated wafer, and the combination was put into a press for a time periodranging from about 90 to about 210 secs after the base material wasmixed. The press was set at a pressure ranging from about 25 to about 60psi. The pressed substrates were removed from the press and solventexchanged using HMDZ/3-pentanone, and then baked at 175° C. and cured at400° C.

EXAMPLE 2

This example illustrates a process wherein a precursor is spin depositedonto a silicon wafer, the wafer is then aged in a chamber for a givenperiod, planarized by pressing the aged (i.e., gelled) nanoporous silicadielectric film against a flat Teflon™ sheet in a press, and then dried.

The aging process in the chamber is as follows. The chamber isevacuated, dosed with water vapor to various pressures for a fixedamount of time, dosed with ammonia gas to a higher pressure for a fixedamount of time, evacuated once again for a fixed time, then the pressurein the chamber is brought to ambient by backfilling with an inert gas. Aprecursor is made by mixing, while stirring, 61 ml tetraethyoxysilane,61 ml tetraethylene glycol, 4.87 ml deionized water, and 0.2 ml 1Mnitric acid (Conc. HNO₃ diluted to 1M. This mixture was then refluxedwhile stirring continuously for 1.5 hours, then cooled. A portion ofthis precursor is diluted 55% by weight with ethanol while stirring.

Approximately 1.5 ml of this diluted precursor is deposited onto a 4inch silicon wafer on a spin chuck, and spun on at 2500 rpm for 10seconds. Two films are deposited in this way. Each film is placed intoan aging chamber, which is then evacuated to 1 mbar (0.76 torr) in 30seconds. Water vapor is dosed into the chamber at a pressure rangingfrom about 7 mbar (5.32 torr) to about 14 mbar (10.64 torr) (from areservoir of deionized water at temperatures ranging from 0° C. to about25° C., respectively); the wafers are left in this pressure range ofwater vapor for 30 seconds.

Ammonia gas is dosed into the chamber to a pressure ranging from about855 mbar (649.8 torr) to about 809 mbar (614.84 torr); the wafers areleft for 1 minute at this pressure range. The chamber is evacuated for30 seconds to 2 mbar (1.52 torr), then immediately backfilled with airto ambient pressure.

The wafers are removed from the chamber, a flat Teflon™ sheet is appliedonto each coated wafer, and the Teflon™ sheeted wafers are put into apress for a time period ranging from about 90 to about 210 secs. Thepress is set at a pressure ranging from about 25 to about 60 psi. Thepressed substrates are removed from the press and placed on a hotplateat 90° C. for 2 minutes, followed by an oven bake at 175° C. for 3minutes, then another oven bake at 400° C. for 3 minutes. The wafers areremoved from the press, and after cooling are measured by ellipsometryfor thickness and refractive index. Refractive index can be linearlycorrelated to the film porosity. A refractive index of 1.0 is 100%porosity and 1.46 is dense, 0% porosity silica. The wafers are alsoinspected by scanning electron microscopy for surface planarity andregularity. The results of the measurements of the nanoporous dielectricfilm confirm that the index of refraction and the thickness are withinacceptable limits, and the surfaces of the dielectric films are planar.

EXAMPLE 3

The processes of Example 1 are repeated, except that the wafers areheated and dried before being placed in the press.

EXAMPLE 4

The processes of Example 1 are repeated, except that the wafers areheated at 90° C. for 2 minutes while still in the press by theapplication of heat to the plates of the press. The wafers are thenremoved from the press for the final oven back as described by Example1.

EXAMPLE 5

The processes of Example 1 are repeated, except that the press is set ata pressure ranging from about 10 to about 30 psi.

EXAMPLE 6

This example illustrates a process wherein a precursor is spin depositedonto a silicon wafer, the wafer is then aged in a chamber for a givenperiod and then dried. The aging process in the chamber is as follows.The chamber is evacuated, dosed with water vapor to a fixed pressure fora fixed amount of time, dosed with ammonia gas to various higherpressures for a fixed amount of time, evacuated once again for a fixedtime, then the pressure in the chamber is brought to ambient bybackfilling with an inert gas. A precursor is made by mixing, whilestirring, 61 ml tetraethyoxysilane, 61 ml tetraethylene glycol, 4.87 mldeionized water, and 0.2 ml 1M nitric acid. This mixture is thenrefluxed while stirring continuously for 1.5 hours, then cooled. Aportion of this precursor is diluted 55% by weight with methanol whilestirring. Approximately 1.5 ml of this diluted precursor is depositedonto a 4 inch silicon wafer on a spin chuck, and spun on at 2500 rpm for10 seconds. Three films are deposited in such a way. Each film is placedinto an aging chamber, which is evacuated to 1 mbar (0.76 torr) in 30seconds. Water vapor is dosed into the chamber to 15 mbar (11.4 torr)(from a reservoir of deionized water at 25° C.) and the wafers are leftfor 30 seconds at this pressure. Ammonia gas is dosed into the chamberto a pressure of 270 mbar (205.2 torr) for the first wafer, 506 mbar(384.56 torr) for the second wafer, and 809 mbar (614.84 torr) for thethird. The wafers are left at these pressures for 3 minutes. Next thechamber is evacuated for 30 seconds to 2 mbar (1.52 torr), thenimmediately backfilled with air back to ambient pressure.

The wafers are removed from the chamber, a flat Teflon™ sheet is appliedonto each coated wafer, and the Teflon™ sheeted wafers are put into apress for a time period ranging from about 200 to about 400 secs. Thepress is set at a pressure ranging from about 40 to about 100 psi. Thepressed substrates are removed from the press and placed on a hotplateat 90° C. for 2 minutes, followed by an oven bake at 175° C. for 3minutes, then another oven bake at 400° C. for 3 minutes. The wafers arethen removed and after cooling are measured by ellipsometry forthickness and refractive index. The wafers are also inspected byscanning electron microscopy for surface planarity and regularity. Theresults of the measurements of the nanoporous dielectric film confirmthat the index of refraction and the thickness are within acceptablelimits, and the surfaces of the dielectric films are planar.

EXAMPLE 7

This example demonstrates that a catalyzed nanoporous silica precursordeposited via codeposition can be aged in ambient clean room humidity toyield low density uniform thin films that can be readily planarized.

The precursor is synthesized by adding 104.0 mL of tetraethoxysilane,47.0 mL of triethylene glycol monomethyl ether, 8.4 mL of deionizedwater, and 0.34 mL of 1N nitric acid together in a round bottom flask.The solution is allowed to mix vigorously then heated to ˜80° C. andrefluxed for 1.5 hours to form a solution. After the solution is allowedto cool, it is diluted 21.6% by weight with ethanol to reduce theviscosity. The catalyst used was monoethanolamine. It is diluted 8.75%by weight in ethanol to reduce viscosity and increase the gel time.

A dual syringe pump is used for deposition. The dual syringes areassembled using a 5 ml and 20 ml syringe, respectively, which are eachattached to a fluid delivery tube. The two tubes each terminate so thatthe fluid streams from each will mix and commingle when the syringes aresimultaneously pumped.

The precursor is loaded into the larger syringe and catalyst is loadedinto the smaller syringe. 1 ml of precursor and 0.346 ml of catalyst aresimultaneously pumped at a rate of 10 ml/min. The fluid streams meet ata 90° angle to form one stream, which in turn flows onto the substrate.The wafer is spun at 2500 rpm for 30 seconds after deposition. The filmis placed in a wafer carrier cartridge in the cleanroom ambient humiditythat is set at 35%. The film is then aged for 15 min.

The film is then solvent exchanged by depositing 20-30 mL of an aged (36hrs) 50/50 (by vol.) mixture of acetone, and hexamethyldisilazane (HMDZ)for 20 seconds at 250 rpm without allowing the film to dry. The film isthen spun dry at 1000 rpm for 5 seconds.

A flat Teflon™ sheet is applied onto the coated wafer, and the Teflon™sheeted wafers are put into a press for a time period ranging from about200 to about 400 secs. The press is set at a pressure ranging from about40 to about 100 psi. The pressed substrates are removed from the pressand then heated at elevated temperatures for 1 min. at 175° C. and 320°C., respectively, in air. The film is characterized by ellipsometry todetermine the refractive index and thickness. In addition, thehydrophobicity is tested by placing a water drop onto the film todetermine the contact angle. The wafers are also inspected by scanningelectron microscopy for surface planarity and regularity. The results ofthe measurements of the nanoporous dielectric film confirm that theindex of refraction and the thickness are within acceptable limits, thatthe films are substantially hyrophobic, and that the surfaces of theproduced dielectric films are planar.

EXAMPLE 8

The processes of Example 7 are repeated, except that the press is set ata pressure ranging from about 10 to about 30 psi.

What is claimed is:
 1. A process for forming a substantially planarizednanoporous dielectric silica coating on a substrate comprising: applyinga composition that comprises a silicon-based precursor onto a substrateto form a coating on a substrate, and conducting the following steps:(a) gelling or aging the applied coating; (b) contacting the coatingwith a planarization object with sufficient pressure to transfer animpression of the object to the coating without substantially impairingformation of nanometer-scale pore structure, (c) separating theplanarized coating from the planarization object, (d) curing saidplanarized coating; wherein steps (a)-(d) are conducted in a sequenceselected from the group consisting of (a), (b), (c), and (d); (a), (d),(b), and (c); (b), (a), (d), and (c); (b), (a), (c), and (d); and (b),(C), (a), and (d).
 2. The process of claim 1 wherein the silicon-baseddielectric precursor is selected from the group consisting of analkoxysilane, alkylalkoxysilane, a silsesquioxane, a hydrogensiloxane, ahydroorganosiloxane, a hydrogensilsesquioxane, an acetoxysilane, ahalogenated silane and combinations thereof.
 3. The process of claim 2wherein the alkoxysilane comprises

wherein at least 2 of the R groups are independently C₁ to C₄ alkoxygroups and the balance, if any, are independently selected from thegroup consisting of hydrogen, alkyl, phenyl, halogen, and substitutedphenyl.
 4. The process of claim 3 wherein each R is independentlyselected from the group consisting of methoxy, ethoxy, propoxy, andbutoxy.
 5. The process of claim 3 wherein the alkoxysilane is selectedfrom the group consisting of tetraethoxysilane, tetramethoxysilane and acombination thereof.
 6. The process of claim 1 wherein the planarizationobject is an object having a contact surface selected from the groupconsisting of a flat surface, a curved surface and combinations thereof,wherein when said planarization object has said curved contact surface,said contacting step is conducted so that said curved contact surface isapplied to said substrate with a rolling motion.
 7. The process of claim6 wherein the planarization object is an optical flat having a contactsurface comprising a layer selected from the group consisting of anon-stick release material, a gas-permeable non-stick release material,a non-stick release material with gas or vapor absorbing properties andcombinations thereof.
 8. The process of claim 7 wherein the non-stickrelease material is separately removable from said planar object contactsurface and the planarized coating.
 9. The process of claim 6 whereinthe planarization object is contacted with the coating of step (a) witha force ranging from about 0.1 MPa to about 1 GPa.
 10. The process claim1 wherein said silicon-based precursor composition further comprises anaging promoter or catalyst selected from the group consisting of water,an acid, a base, a combination of water and an acid, and a combinationof water and a base.
 11. The process of claim 10 wherein steps (a)-(d)are conducted in the sequence of (b), (a), (c) and (d).
 12. The processof claim 10 wherein the base is a non-volatile amine selected from thegroup consisting of primary, secondary and tertiary alkylamines, arylamines, alcohol amines and mixtures thereof which have a boiling pointof about 200° C. or less.
 13. The process of claim 1 wherein curing step(d) is conducted by heating the coating while in contact with theplanarization object.
 14. The process of claim 1 wherein the coating isformed and applied onto the substrate by a combined stream process whichcomprises performing either (i) or (ii): (i) (A) combining a stream ofan alkoxysilane composition with a stream of a base containing catalystcomposition to form a combined composition stream which is unbounded ata point of confluence; and  conducting steps (B) and (C) in either orderor simultaneously:  (B) immediately depositing the combined compositionstream onto a surface of the substrate;  (C) exposing the combinedcomposition to water; and (ii) (A) combining a stream of an alkoxysilanecomposition with a stream of water to form a combined composition streamwhich is unbounded at a point of confluence; and  (B) immediatelydepositing the combined composition stream onto a surface of thesubstrate.
 15. The process of claim 1 wherein the coating is appliedonto the substrate by a method selected from the group consisting ofspin-coating, dip coating, brushing, rolling, spraying, chemical vapordeposition and combinations thereof.
 16. The process of claim 1 whereinthe curing of step (d) is conducted by steps selected from the groupconsisting of heating, drying, evaporating and combinations thereof. 17.The process of claim 16 wherein the heating step is conducted at atemperature ranging from about 350° C. to about 600° C. for a timeperiod ranging from about 30 seconds to about 5 minutes.
 18. The processclaim 1 wherein the silicon-based precursor composition comprises atleast one organic solvent.
 19. The process of claim 1 wherein thecoating is contacted with the planarization object under vacuum.
 20. Theprocess of claim 1 wherein the substrate comprises at least onesemiconductor material.
 21. The process of claim 1 further comprising astep of treating the nanoporous dielectric silica coating with a surfacemodification agent under conditions sufficient to render the coatinghydrophobic.
 22. The process of claim 21 wherein the surfacemodification agent comprises hexamethyldisilazane.
 23. The process ofclaim 1 further comprising a subsequent step of forming an integratedcircuit from the planarized nanoporous dielectric silica coating. 24.The process of claim 1 wherein the process steps (a)-(d) are conductedin the order of (b), (a), (c), and (d).
 25. The process of claim 1further comprising a subsequent step of forming an integrated circuitfrom the patterned dielectric silica coating.
 26. The process of claim 1wherein the planarization object is an object having a flat contactsurface.
 27. A process for forming a dielectric silica coating on asubstrate with a pattern impressed thereon comprising coating asubstrate with a composition comprising a precursor for forming ananoporous dielectric film, contacting said coating with a patternedsurface with a pressure and for a time period sufficient in impress thepattern on said coating, and then separating the patterned surface fromsaid coating.
 28. The process of claim 27 wherein said coating is agedor gelled while said patterned surface is in contact with said coating.29. The process of claim 27 wherein said coating is aged or gelled aftersaid patterned surface is removed from contact with said coating. 30.The process of claim 27 wherein said coating is aged or gelled beforesaid patterned surface is contacted with said coating.
 31. The processof claim 27 wherein said patterned surface comprises at least one regionthat is at least 98 percent planar.
 32. The process of claim 27 whereinsaid patterned surface has multiple planar regions.
 33. A method ofplanarizing or patterning a dielectric film on a substrate comprising(a) applying a dielectric film precursor to a substrate by chemicalvapor deposition; (b) planarizing or patterning said dielectric film inan apparatus comprising (i) a press for applying contact pressure to acompression tool, (ii) a compression tool having a working face that isplanar or patterned, wherein said compression tool is operably connectedto said press, (iii) a controller for regulating the position, timingand force applied to said dielectric film by said press, (iv) a supportpositioned adjacent said substrate and opposite from the film to becontacted with the compression tool; by applying sufficient pressure totransfer an impression of the working face of the compression tool tothe coating; (c) gelling said dielectric film before, during or afterstep (b); (d) curing said dielectric film.
 34. A method of planarizingor patterning a dielectric film on a substrate comprising (a) applying adielectric film precursor to a substrate; (b) planarizing or patterningsaid dielectric film in an apparatus comprising (i) a press for applyingcontact pressure to a compression tool, (ii) a compression tool having aworking face that is planar or patterned, wherein said compression toolis operably connected to said press, (iii) a controller for regulatingthe position, timing and force applied to said dielectric film by saidpress, (iv) a support positioned adjacent said substrate and oppositefrom the dielectric film to be contacted with the compression tool; byapplying sufficient pressure to transfer an impression of the workingface of the compression tool to the coating; (c) gelling said dielectricfilm before, during or after step (b); (d) curing said dielectric filmwherein said curing comprises processing by electron beam, ion beam,ultraviolet radiation, or ionizing radiation.